Voyager missions: Twins that changed how we discern space giants

The two manmade objects most distant from Earth are slowly powering down. By 2025 or perhaps a little later, the Voyager twins will be completely bereft of po­­wer. However, both the spacecraft will keep travell­ing, heading further and further out of the Solar System.

The Voyager saga showcases in­credible engineering. Neither spa­ce­craft was expected to be functional for more than five years but it’s 44 years and counting. They have sent back huge amounts of data, and breathtaking images, which revolutionised our understanding of gas giants, ice giants, dwarf planets, weird rings and moons.

The mission idea sparked in 1965. A young aerospace engineer at Caltech, Gary Flandro made an interesting calculation. The outer planets — Jupiter, Saturn, Uranus and Neptune — would be lined up in what was almost a straight line in the late 1970s and early ’80s. The planets travel in roughly egg-shaped (elliptical) orbits around the sun. But they have different velo­cities and of course, they are at varying distances. This phenomenon, where these specific planets are in a roughly straight line, occurs only every 176 years or so.

Flandro realised there could be an interesting payoff for exploration. If you launched a spacecraft towards Jupiter, and timed and aimed perfectly, it would benefit from a slingshot effect. The gravitational pull of Jupiter would add to its speed, and push it out faster towards Saturn. Similarly, Saturn would offer a gravitational assist to speed the craft on to Uranus and Uranus would speed it on to Neptune. A 30-year journey to reach Neptune could be cut to less than 12 years by boosts.

This led to the Voyager Missions. Voyager 1 and 2 were launched within 15 days of each other in August-September 1977. (Voyager 1 launched after Voyager 2 but was named V1 because it would reach Jupiter first). They would reach Jupiter in March 1979 and July 1979, and Saturn in November 1980. After that, Voyager 1 would travel “up” out of the Solar System while Voyager 2 would fly by Uranus (January 86) and Neptune (Aug­ust 1989) and then go “down”. “Up” and “down” is with reference to the solar system’s orientation. The planets orbit in a plane called the ecliptic. Voyager 1 headed above the ecliptic, while Voyager 2 headed down.

Both craft kept coming up with surprises. They discovered multiple new moons of all the planets, they found volcanic activity on moons, and they found that Jupiter, Uranus and Neptune also had rings. They found Saturn’s moon Titan had a thick atmosphere and Jupiter’s Great Red Spot was a monstrous perpetual storm. They also discovered huge magnetic activity around Jupiter.

Voyager 2 found the ice-giant Uranus was full of surprises. The coldest planet has a unique blue-green colour. It has at least 11 moons (six new ones), it has rings; it has a weird magnetic field and it spins on its side. (My minority view is that Uranus is the most beautiful planet in the Solar System but most folks think Saturn wins the beauty cont­est and of course, Uranus’ name leads to crude jokes). Neptune is another ice-giant — deeper-blue. It also has a lot of moons and rings, and pink geysers. After the Neptune fly-by, Voyager 2 turned off its camera to conserve power and headed “down”.

The last images came in from Voyager 1 from a distance of 6 billion km, showing Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune in array. After that both craft have sent radio data but no visual images. In 2012, Voyager 1 left the Solar System, and Voyager 2 left the Solar System in 2018. Since then, they’ve been studying phenomena like cosmic rays, magnetic fields, interstellar and solar winds (charged particles flowing from stars are called wind).

Both craft work off plutonium reactors and the fuel will eventually run out. Both connect via radio to NASA’s Deep Space network. They are now around 20-21 light-hours away, which means radio communication takes twice as long. As the mission has progressed, instruments have been progressively shut down to conserve power.

The on-board computers were state-of-the-art with 69 kilobytes of memory, approximately one-milli­onth the capacity of a high-end sm­a­rtphone. The data is collected on tape recorders and sent back by a 23-watt transmitter — think of a ref­rigerator light. They have 3.5-metre dish antennas to amplify signals. Voyager 1 seems a little confu­sed as to where it is at the moment, which has led optimists to hope it’s been hacked. It does carry a gold-plated disc with multilingual conte­nt inclu­ding songs and images. Who knows, someday, sometime, that might intrigue an intelligent al­ien if it does meet one and gets hacked.